Version 10.2.0.5599 (32 Bit)
It seems as if when a column is changed from
No Default Value it runs a query to set it to
NULL instead of just removing the default.
Here is what gets executed when trying to change it:
ALTER TABLE `game_store` ALTER `game_id` DROP DEFAULT; ALTER TABLE `game_store` CHANGE COLUMN `game_id` `game_id` INT(10) UNSIGNED NULL AFTER `id`;